Process for dry spinning polybenzimidazoles



United States Patent 3,502,756 PROCESS FOR DRY SPINNING POLYBENZIMIDAZOLES Thomas C. Bohrer, Charlotte, NC, and Arnold J. Rosenthal, Whippany, N.J., assignors to Celanese Corporation, New York, N.Y., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 519,299, Jan. 7, 1966. This application Mar. 17, 1969, Ser. No. 807,927

Int. Cl. D01d 5/04; D01f 7/00 US. Cl. 26485 15 Claims ABSTRACT OF THE DISCLOSURE An improved process is provided for the dry spinning of a filament forming polybenzimidazole. A solution of a polybenzimidazole dissolved in a solvent selected from the group consisting of dimethylacetamide, dimethyl sulfoxide, N,N-dimethylformamide, and N-methyl-Z-pyrrolidone is dry spun into an evaporative medium of superheated steam to form a polybenzimidazole filament which may exhibit superior physical properties. The explosion hazard which is normally encountered when using these common polybenzimidazole dry spinning solvents at elevated temperatures is effectively eliminated.

Cross-reference to related application This is a continuation-in-part of our Ser. No. 519,299 filed Ian. 7, 1966, now abandoned.

Background of the invention The invention relates to an improved process for dry spinning a solution of a polybenzimidazole to form a polybenzimidazole filament. Commonly utilized spinning solvents for polybenzimidazoles such as dimethylacetamide, dimethyl sulfoxide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone present explosion hazards when present with oxygen at elevated temperatures.

It has accordingly been deemed essential in prior art processes that such polybenzimidazole solutions be spun into a cabinet containing an inert gaseous atmosphere, such as nitrogen. However, in a commercial operation such a procedure requires nitrogen purification and recycle which complicates and increases the cost of solvent recovery.

The prior art has taught the possibility of spinning ce'llu losic and related filament forming substances into steam. See, for instance, US. Patent No. 2,142,121 to Dreyfus. In such instances, the filament forming substance and spinning solvent for the same have been dissimilar to those employed in the present process. Also, various filament forming solutions have been spun into superheated organic vapors in the past for the purpose of slowing down coagulation.

It is an object of the invention to provide an improved process for the dry spinning of a filament forming polybenzimidazole. I

It is another object of the invention to provide a process for the dry spinning of a filament forming polybenzimidazole in which solvent recovery is readily facilitated.

These and other objects of the invention, as well as the scope, nature, and utilization of the invention, will be apparent from the following detailed description and appended claims.

Summary of the invention It has been found that an improved process for dry spinning a polybenzimidazole comprises extruding a solution of a filament forming polybenzimidazole utilizing a 3,502,756 Patented Mar. 24, 1970 ice Detailed description of the invention According to the polybenzimidazole spinning method of the present invention, the need for inert gas recycle or purification is eliminated and solvent recovery is simplified. The present method also alters the drying rate and in some cases provides a superior polybenzimidazole fiber.

According to the method of the present invention the polybenzimidazole spinning solution is spun into superheated steam. The conditions for employing the superheated steam are not critical exept that they should not be so extreme as to cause it to rain on the emergent polybenzimidazole filament. The non-uniform application of droplets results in non-uniform fiber properties.

In a preferred mode of operation the superheated steam at pressures up to 15 p.s.i.g. is introduced to a superheater and permitted to expand to atmospheric pressure and upon exiting from the superheater is introduced to the spinning cabinet at jet level. The temperature at this point may be as low as C. or as high as 300 C. depending upon the solvent and spinning system being employed. The temperature at the exit end of the cabinet is at least equal to or preferably substantally higher than at the entrance end of the cabinet and should always remain above 100 C. This prevents condensation of water as a result of the cooling accompanying solvent evaporation. The spinning cabinet is essentially free of air or gaseous oxygen while the spinning process is conducted.

The polymers which are spun according to the present process are the fiber-forming (fiber-formable) linear polybenzimidazoles. Typical polymers of this class and their preparation are more fully described in US. Patents Nos. 2,895,948 to Brinker et al. and 3,174,947 to Marvel et al., and in the Journal of Polymer Science, vol. 50, pages 511- 5 39 1961). As indicated in the Marvelet al. patent at col. 7, lines 58-62, suitable polybenzimidazole solvents include dimethyl sulfoxide and N,N-dimethylformamide.

An especially interesting subclass of polybenzimidazoles for fiber production consists essentially of recurrin units of the formula:

wherein R is a tetravalent aromatic nucleus preferably symmetrically substituted, with nitrogen atoms forming the benzimidazole rings paired upon adjacent carbon atoms of the said aromatic nucleus and R' is a member of the class consisting of (1) an aromatic ring, (2) an alkylene group (preferably those having from 4 to 8 carbon atoms), and (3) a heterocyclic ring from the class consisting of (a) pyridine, (b) pyrazine, (c) furan and (d) quinoline. In a preferred embodiment of the invention fibers are prepared from aromatic polybenzimidadoles, i.e. polymers from classes (1) and (3) wherein R is an aromatic ring or a heterocyclic ring. Preferred R groups are 3,3,4,4'-biphenylene,

Examples of such polybenzimidazoles include poly-2,2- (pyridylene 3",5") 5,5 bibenzimidazole; poly- 2,2- (furylene-2,5") 5,5 bibenzimidazole; poly-2,2-(bipheny1ene-4",4) 5,5 bibenzimidazole; poly-2,2-amylone-5,5'-bibenzimidazole; poly 2,2 octamethylene-5,5'- benzimidazole; poly2,2-hexamethylene 5,5 di(benzimidazole)propane-2,2; and poly 2,6 (m-phenylene)-diimidazobenzene. The particularly preferred polybenzimidazole is poly[2,2'-(mphenylene)-5,5'-bibenzimidazole].

In the instant process the spinning solution of a filament forming polybenzimidazole is formed with a solvent selected from the group consisting of dimethylacetamide, dimethyl sulfoxide, N,N-dimethylformamide, and N-methyl- 2-pyrrolidone. The polybenzimidazole is commonly present in these solvents in concentration of about 20 to 35 percent by weight. The explosion hazard which is normally encountered when using these common polybenzimidazole dry spinning solvents at elevated temperatures is eifectively eliminated.

The solvent from the spinning solution can be recovered from the vapor stream leaving the column by cooling to room temperature to effect condensation, followed by separation. By contrast, when an inert gas such as nitrogen is employed as the gaseous evaporative medium, room temperature cooling of the exit gas will leave too much solvent in the nitrogen which is intended for recycle. Consequently more severe cooling is necessary along with use of absorption beds such as carbon to remove further quantities of solvent from the nitrogen prior to recycle. Thus the present invention affords a safe, simple, and economic method of dry spinning polybenzimidazole fibers having desirable properties.

The following examples are given as specific illustrations of the invention. It should be understood, however, that the invention is not limited to the specific details set forth in the examples.

EXAMPLE 1 Poly[2,2'-(maphenylene)-5,5'-bibenzimidazole] in a dimethylacetamide dope (solids concentration-33 percent by weight, viscosity 9600 poise at 20 C.) is extruded at a temperature of 143 C. through a jet containing ten holes (each .076 mm. in diameter) into an enclosed 23-foot downdraft column in which superheated steam is the drying atmosphere. Steam at about p.s.i.g. is fed to a superheater, heated to 300 C., and around a candle filter down the heated column (top148 C., bottom-210 C.) and exhausted. The yarn is withdrawn from the cabinet at a speed of 100 meters per minute and is thereafter drawn in steam at a ratio of 1.1:1. The thus-produced yarn has a denier of 122, a tenacity of 1.7 grams per denier, and 110 percent elongation; further drawing at a temperature of 500 C. and a draw ratio of 2.1:1 results in a tenacity of 5 grams per denier and 20 percent elongation.

The resulting polybenzimidazole filaments have a dogbone cross section whereas polybenzimidazole filaments spun under generally similar conditions into a nitrogen atmosphere have a multilobal cross section. A dogbone cross section promotes more stable spinning and drawing.

EXAMPLE II Example I may be repeated substituting a dimethyl sulfoxide dope for the dimethylacetamide dope and maintaining the heated column at 175 C. at the top and at 4 220 C. at the bottom to produce substantially similar results.

EXAMPLE HI Example I may be repeated substituting a N,N-dimethylformamide dope for the dimethylacetamide dope to produce substantially similar results.

EXAMPLE IV Example I may be repeated substituting a N-methyl-2- pyrrolidone dope for the dimethylacetamide dope and maintaining the heated column at 190 C. at the top and at 250 C. at the bottom to produce substantially similar results.

Although the invention has been described with preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art.

We claim:

1. An improved process for dry spinning a polybenzimidazole comprising extruding a solution of a filament forming polybenzimidazole utilizing a solvent selected from the group consisting of dimethylacetamide, dimethyl sulfoxide, N,N-dimethylformamide, and N-methyl-Z- pyrrolidone into an evaporative medium of superheated steam having a temperature of about C. to 300 C.

2. A process according to claim 1 wherein said polybenzimidazole consists essentially of recurring units of the formula:

wherein R is a tetravalent aromatic nucleus, with the nitrogen atoms forming the benzimidazole rings paired upon adjacent carbon atoms of said aromatic nucleus and R is selected from the group consisting of (1) an aromatic ring, (2) an alkylene group having from 4 to 8 carbon atoms, and (3) a heterocyclic ring selected from the group consisting of (a) pyridine, (b) pyrazine, (c) furan and (d) quinoline.

3. A process according to claim 1 wherein said solvent utilized in said solution of filament forming polybenzimidazole is dimethylacetamide.

4. A process according to claim 1 wherein said filament forming polybenzimidazole is poly[2,2'-(m-phenylene)- 5,5 '-bibenzimidazole] 5. A process according to claim 4 wherein said solvent utilized in said solution of filament forming polybenzimidazole is dimethylacetamide.

6. A process according to claim 4 wherein said solvent utilized in said solution of filament forming polybenzimidazole is dimethyl sulfoxide.

7. A process according to claim 4 wherein said solvent utilized in said solution of filament forming polybenzimidazole is N,N-dimethylformamide.

8. A process according to claim 4 wherein said solvent utilized in said solution of filament forming polybenzimidazole is N-methyl-2-pyrrolidone.

9. An improved process for dry spinning a filament forming polybenzimidazole consisting essentially of recurring units of the formula:

wherein R is a tetravalent aromatic nucleus, with the nitrogen atoms forming the benzimidazole rings paired upon adjacent carbon atoms of said aromatic nucleus and R is selected from the group consisting of (1) an aromatic ring, (2) an alkylene group having from 4 to 8 carbon atoms, and (3) a heterocyclic ring selected from the group consisting of (a) pyridine, (b) pyrazine, (c) furan and (d) quinoline; said process comprising extruding a solution of said polybenzimidazole containing said polybenzimidazole in a concentration of about 20 to 35 percent by weight and utilizing a solvent selected from the group consisting of dimethylacetamide, dimethyl sulfoxide, N,N-dimethylformamide, and N-methyl-Z-pyrrolidone into an evaporate medium of superheated steam having a temperature of about 100 C. to 300 C.

10. A process according to claim 9 wherein said solvent utilized in said solution of filament forming polybenzimidazole is dimethylacetamide.

11. A process according to claim 9 wherein said filament forming polybenzimidazole is poly[2,2-(m-phenylene -5 ,5 '-bibenzimidazole] 12. A process according to claim 11 wherein said solvent utilized in said solution of filament forming polybenzimidazole is dimethylacetamide.

13. A process according to claim 11 wherein said solvent utilized in said solution of filament forming polybenzimidazole is dimethyl sulfoxide.

14. A process according to claim 11 wherein said solvent utilized in said solution of filament forming polybenzimidazole is N,N-dimethylformamide.

15. A process according to claim 11 wherein said solvent utilized in said solution of filament forming polybenzimidazole is N-methyl-Z-pyrrolidone.

References Cited UNITED STATES PATENTS 2,032,606 3/ 1936 Whitehead 188 2,035,872 3/1936 Ezzard et a1 18-8 2,142,121 1/1939 Dreyfus 18-8 2,161,354 6/1939 Imray et al. 264207 2,472,842 6/1949 Mouchiroud et al. 264205 2,761,754 9/1956 Jones et al. 264169 3,174,947 3/1965 Marvel et al. 26078 3,415,782 12/1968 Irwin et a1. 264205 3,441,640 4/1969 Santangelo 264203 OTHER REFERENCES The Condensed Chemical Dictionary, 1961, 6th ed., New York, Reinhold Publishing Corp., pp. 392 and 1119.

0 JULIUS FROME, Primary Examiner H. MINTZ, Assistant Examiner 

